Signal transmitter and signal receiver

ABSTRACT

In a signal transmitter and a signal receiver, a multiplexing part multiplexes a video signal and a time-base-compressed audio signal on the basis of a multiplexing control signal to transmit the multiplexed signal through a data line in the signal transmitter. Further, a demultiplexing part demultiplexes a video/audio multiplexed signal received through the data line into the original video signal and audio signal by a demultiplexing control signal in the signal receiver. According to the so-configured signal transmitter and signal receiver, it is possible to realize a signal transmission system compliant with the DVI standard, in which the audio signal as well as the video signal can be transmitted.

This application is a divisional application of application Ser. No.10/088,586, filed Jul. 9, 2002 now U.S. Pat. No. 7,379,121 which is aNational Stage Application of International Application No.PCT/JP2001/06339, filed Jul. 23, 2001.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a signal transmitter and a signalreceiver.

2. Background Art

A conventional signal transmission system according to DVI (DigitalVisual Interface) standard will be described with reference to FIG. 26.FIG. 26 is a diagram illustrating a structure of the conventionaltransmission system.

In FIG. 26, numerals 2601 to 2603 denote TMDS encoders/serializersprovided at the transmitting end, which TMDS-encode inputted componentsignals such as RED, GREEN, and BLUE signals, serialize the encodedsignals, and output the same to transmission lines. Numerals 2604 to2606 denote TMDS decoders/recoverers provided at the receiving end,which TMDS-decode the received signals, recover the decoded signals, andrestore the component signals.

A DE (Data Enable) signal is a signal indicating a period during whichthe component signal such as RED, GREEN, and BLUE signals exists, andthis is a HIGH active signal. For example, the DE signal is LOW in aperiod of a horizontal synchronizing signal or vertical synchronizingsignal of video.

CTL (Control) signals CTL 0, CTL 1, CTL 2, and CTL 3 are prepared ascontrol signals. However, these signals are not in use in the presentDVI standard. More specifically, the levels of the signals are always 0.

The so-configured conventional signal transmission system will bedescribed.

The TMDS encoders/serializers 2601 to 2603 at the transmitting endconvert video signals (RGB signals) inputted at 8 bits into signals of10 bits, serialize the converted signals, and output them totransmission lines. The object of the 8-to-10 bit conversion is toreduce data changing points and convert the data into a format that issuitable for high-speed transmission. Further, the TMDSencoders/serializers 2601 to 2603 convert the 2 bit-CTL signals into 10bit-CTL signals and transmit the converted CTL signals to thetransmission lines. The DE signals are also encoded, serialized, andtransmitted to the transmission lines.

The TMDS decoders/recoverers 2604 to 2606 at the receiving end decode10-bit serial data received through the transmission lines into the8-bit color signals, the DE signals, and the 2-bit CTL signals todecompress the signals.

However, the DVI standard is a standard for transmitting only videosignals, and the conventional signal transmission system cannot transmitaudio signals.

The present invention is made to solve the above-mentioned problem andhas for its object to provide a signal transmitter and a signal receiverthat can realize a signal transmission system according to the DVIstandard in which audio signals as well as video signals can betransmitted.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda signal transmitter which is connected to a signal receiver via atransmission line. The signal transmitter includes: a time-basecompression means for time-base-compressing a first signal; amultiplexing control signal generator for generating a multiplexingcontrol signal on the basis of a second signal; a signal multiplexingmeans for multiplexing the time-base-compressed first signal, the secondsignal and a third signal, employing the multiplexing control signalgenerated by the multiplexing control signal generator, and outputting amultiplexed signal; and a signal transmitting means for transmitting themultiplexed signal and the multiplexing control signal to the signalreceiver.

Therefore, it is possible to realize a signal transmission system whichtransmits the first, second and third signals through the sametransmission line.

According to a second aspect of the present invention, there is provideda signal transmitter which is connected to a signal receiver via atransmission line, wherein the signal transmitter includes: a time-basecompression means for time-base-compressing a first signal; amultiplexing control signal generator for generating a multiplexingcontrol signal on the basis of a second signal; a signal multiplexingmeans for multiplexing the time-base-compressed first signal, the secondsignal and a third signal, employing the multiplexing control signalgenerated by the multiplexing control signal generator, and outputting amultiplexed signal; and a signal transmitting means for transmitting themultiplexed signal to the signal receiver.

Therefore, it is possible to realize a signal transmission system whichtransmits the first, second and third signals through the sametransmission line, without transmitting the multiplexing control signalto the signal receiver.

According to a third aspect of the present invention, in the signaltransmitter as defined in the first or second aspects, the first signalis an audio signal, the second signal is a horizontal synchronizingsignal or a vertical synchronizing signal, and the third signal is avideo signal.

Therefore, it is possible to realize a signal transmission systemaccording to DVI standard, which can transmit the audio signal as wellas the video signal.

According to a fourth aspect of the present invention, there is provideda signal transmitter according to DVI transmission standard whichtransmits RGB video signals as serial data having: a first mode oftransmitting the RGB video signals as serial data, and a second mode oftransmitting three signals corresponding to a luminance signal, a colordifference signal and an audio signal, and comprising a switching meansfor switching between the first mode and the second mode.

Therefore, it is possible to realize a signal transmission systemaccording to the DVI standard, which can transmit the audio signal aswell as the video signal.

According to a fifth aspect of the present invention, there is provideda signal receiver which is connected to a signal transmitter via atransmission line, wherein the signal receiver includes: a firstreceiving means for receiving a multiplexed signal in which atime-base-compressed first signal, a second signal, and a third signalare multiplexed, from the signal transmitter; a second receiving meansfor receiving a multiplexing control signal from the signal transmitter;a demultiplexing means for demultiplexing the multiplexed signalreceived by the first receiving means into the first and second signals,employing the multiplexing control signal received by the secondreceiving means; and a time-base decompression means fortime-base-decompressing the first signal obtained by the demultiplexingmeans.

Therefore, it is possible to realize a signal transmission system whichtransmits the first, second, and third signals through the sametransmission line.

According to a sixth aspect of the present invention, there is provideda signal receiver which is connected to a signal transmitter via atransmission line, wherein the signal receiver includes: a receivingmeans for receiving a multiplexed signal in which a time-base-compressedfirst signal, a second signal and a third signal are multiplexed, fromthe signal transmitter; a detection means for detecting the secondsignal from the multiplexed signal; a multiplexing control signalgenerating means for generating a multiplexing control signal on thebasis of the second signal detected by the detection means; ademultiplexing means for demultiplexing the multiplexed signal into thefirst, second and third signals, employing the multiplexing controlsignal; and a time-base decompression means for time-base-decompressingthe first signal obtained by the demultiplexing means.

Therefore, it is possible to realize a signal transmission system whichcan demultiplex the multiplexed signal and receive the first, second andthird signals through the same transmission line, without receiving themultiplexing control signal from the signal transmitter.

According to a seventh aspect of the present invention, in the signalreceiver as defined in the fifth or sixth aspects, the first signal isan audio signal, the second signal is a horizontal synchronizing signalor a vertical synchronizing signal, and the third signal is a videosignal.

Therefore, it is possible to realize a signal transmission systemaccording to the DVI standard, which can transmit the audio signal aswell as the video signal.

According to an eighth aspect of the present invention, there isprovided a signal receiver according to DVI transmission standard whichreceives RGB video signals as serial data having: a first mode ofreceiving the RGB video signals as serial data and a second mode ofreceiving three signals corresponding to a luminance signal, a colordifference signal and an audio signal, and comprising a switching meansfor switching between the first mode and the second mode.

Therefore, it is possible to realize a signal transmission systemaccording to the DVI standard, which can transmit the audio signal aswell as the video signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a structure of a signal transmissionsystem according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a video signaland an audio signal before time-base compression.

FIG. 3 is a diagram for explaining a horizontal synchronizing signal anda vertical synchronizing signal.

FIG. 4 is a diagram illustrating a structure of a time-base compressionpart of the signal transmission system according to the firstembodiment.

FIG. 5 is a diagram for explaining time-base compression in the signaltransmission system according to the first embodiment.

FIG. 6 is a diagram illustrating a structure of a multiplexing part ofthe signal transmission system according to the first embodiment.

FIG. 7 is a diagram illustrating a state of multiplexing of a videosignal and an audio signal in the signal transmission system accordingto the first embodiment.

FIG. 8 is a diagram illustrating a structure of a demultiplexing part ofthe signal transmission system according to the first embodiment.

FIG. 9 is a diagram illustrating a state of demultiplexing into thevideo signal and the audio signal in the signal transmission systemaccording to the first embodiment.

FIG. 10 is a diagram illustrating a structure of a time-basedecompression part of the signal transmission system according to thefirst embodiment.

FIG. 11 is a diagram for explaining time-base decompression in thesignal transmission system according to the first embodiment.

FIG. 12 is a diagram illustrating a structure of a signal transmissionsystem according to a second embodiment.

FIG. 13 is a diagram illustrating a structure of a time-base compressionpart of the signal transmission system according to the secondembodiment.

FIG. 14 is a diagram for explaining time-base compression in the signaltransmission system according to the second embodiment.

FIG. 15 is a diagram illustrating a state of multiplexing of a videosignal and an audio signal in the signal transmission system accordingto the second embodiment.

FIG. 16 is a diagram illustrating a structure of a demultiplexing partof the signal transmission system according to the second embodiment.

FIG. 17 is a diagram illustrating a state of demultiplexing into thevideo signal and the audio signal in the signal transmission systemaccording to the second embodiment.

FIG. 18 is a diagram illustrating a structure of a time-basedecompression part of the signal transmission system according to thesecond embodiment.

FIG. 19 is a diagram for explaining time-base decompression in thesignal transmission system according to the second embodiment.

FIG. 20 is a diagram illustrating a structure of a signal transmissionsystem according to a third embodiment.

FIG. 21 is a diagram illustrating a state of data in the signaltransmission system according to the third embodiment.

FIG. 22 is a diagram illustrating an audio separation method at thereceiving end in the signal transmission system according to the thirdembodiment.

FIG. 23 is a diagram illustrating a decoding method at the receiving endin the signal transmission system according to the third embodiment.

FIG. 24 is a diagram illustrating a structure of a signal transmissionsystem according to a fourth embodiment.

FIG. 25 is a diagram illustrating a signal image on a transmission linein the signal transmission system according to the fourth embodiment.

FIG. 26 is a diagram illustrating a structure of a conventional signaltransmission system.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The embodiments described here are onlyillustrative and the present invention is not restricted to theseembodiments.

Embodiment 1

Hereinafter, a signal transmission system according to a firstembodiment will be described with reference to FIGS. 1 to 11.

FIG. 1 is a diagram illustrating a structure of the signal transmissionsystem according to the first embodiment.

In FIG. 1, a signal transmitter (transmitting end) comprises a time-basecompression part 101, which compresses an audio signal on a time axis,and a multiplexing part 102, which multiplexes a video signal and atime-base compressed audio signal employing a multiplexing controlsignal and outputs a video/audio multiplexed signal to a data line 106(which will be described later).

A signal receiver (receiving end) comprises a demultiplexing part 103,which demultiplexes the video/audio multiplexed signal in which thevideo signal and the audio signal are multiplexed, and which has beenreceived through the data line 106, employing the multiplexing controlsignal. The signal receiver also includes a time-base decompression part104, which time-base decompresses the audio signal obtained by thedemultiplexing part 103 to restore the original audio signal, and anaudio clock reproduction part 105, which reproduces an audio clock onthe basis of video clocks received from the transmitting end through aclock line 107.

The data line 106 is a serial transmission line connecting the signaltransmitter and the signal receiver.

Here, the multiplexing control signal controls so as to multiplex theaudio signal in a blank period of the video signal such as a horizontalsynchronizing period and a vertical synchronizing period of the videosignal, and the multiplexing control signal is generated by amultiplexing control signal generator (not shown).

Next, an operation of the signal transmission system according to thefirst embodiment will be described.

First, a relationship between the video signal and the audio signalbefore the time-base compression is schematically shown in FIG. 2. Sincethe video signal generally has a larger amount of data than the audiosignal, several samples of the video signal temporally correspond toapproximately one sample of the audio signal. In the signal transmissionsystem according to the first embodiment, this audio signal istemporally compressed and multiplexed into an area where the videosignal does not exist. More specifically, the time when the video signaldoes not exist is, for example, a horizontal synchronizing period orvertical synchronizing period of the video signal as shown in FIG. 3. InFIG. 3, a hatched section other than an effective screen corresponds tothe synchronizing period. In FIG. 3, a SD screen of MP@ML (Main ProfileMain Level) of MPEG 2 is taken as an example. The whole screen comprises858 pixels (horizontal direction)×525 lines (vertical direction). Of thewhole screen, the effective screen comprises 720 pixels (horizontaldirection)×480 lines (vertical direction), and a difference between thewhole screen and the effective screen is a synchronizing period. Theaudio signal is multiplexed in this synchronizing period.

Next, an operation at the transmitting end will be described.

FIG. 4 is a diagram illustrating a structure of the time-basecompression part 101. The time-base compression part 101 is constitutedmainly by a memory, and converts a rate of an inputted audio signal.More specifically, a sampling clock of the input is an audio clock faand a clock of the output is a video clock fv. Here, fa refers to anaudio sampling clock frequency and fv refers to a video sampling clockfrequency. Further, the multiplexing control signal is employed tocontrol the output of the time-base compression part (memory) 101. Asthis multiplexing control signal, the horizontal synchronizing signal orthe vertical synchronizing signal is employed.

FIG. 5 is a diagram illustrating a state of time-base compression by thetime-base compression part 101. The audio signal before time-basecompression is inputted at the sampling frequency fa and the audiosignal after the time-base compression is outputted to the multiplexingpart 102 at the sampling frequency fv. The audio signal after thetime-base compression is outputted in a period during which themultiplexing control signal is LOW. In FIG. 5, for simplification, areduced number of audio sample points which are outputted in a periodduring which the multiplexing control signal is LOW are shown, while theactually outputted audio sample points are far more than these.

FIG. 6 is a diagram illustrating a structure of the multiplexing part102. The multiplexing part 102 multiplexes the video signal and thetime-base-compressed audio signal, and outputs a video/audio multiplexedsignal. Inputs of the video signal and the time-base-compressed audiosignal to the multiplexing part 102 are switched in accordance with themultiplexing control signal. For this multiplexing control signal, thehorizontal synchronizing signal or vertical synchronizing signal of thevideo is employed.

FIG. 7 illustrates a state of multiplexing of a video signal and anaudio signal by the multiplexing part 102. In FIG. 7, the upper twolines indicate a video signal and an audio signal after time-basecompression. A white circle indicates a sampling point of the videosignal and a black circle indicates a sampling point of the audiosignal. The lowest line indicates a state where the audio signal ismultiplexed onto the video signal in a period during which themultiplexing control signal is LOW. This video/audio multiplexed signalis a signal for a transmission line, and is outputted to thetransmission line.

Next, an operation at the receiving end will be described.

FIG. 8 is a diagram illustrating a structure of the demultiplexing part103. The demultiplexing part 103 demultiplexes the video/audiomultiplexed signal that has been transmitted through the data line 106into a video signal and a time-base compressed audio signal. While ademultiplexing control signal is employed for the demultiplexing, themultiplexing control signal which is supplied from the transmitting endthrough a transmission line provided apart from the data line 106 isemployed as this demultiplexing control signal.

FIG. 9 is a diagram illustrating a state of the demultiplexing of thevideo signal and the audio signal by the demultiplexing part 103. Thevideo/audio multiplexed signal transmitted through the data line 106 isdemultiplexed into a video signal and an audio signal in accordance withthe demultiplexing control signal. More specifically, a signal during aperiod in which the demultiplexing control signal is LOW is taken as thetime-base-compressed audio signal, and a selector of the demultiplexingpart 103 shown in FIG. 8 is set toward the side of the audio signaloutput.

FIG. 10 is a diagram illustrating a structure of the time-basedecompression part 104. The time-base decompression part 104 isconstituted mainly by a memory, and it receives the time-base-compressedaudio signal at the video sampling clock fv in a period during which thedemultiplexing control signal is LOW and outputs the audio signal at theaudio sampling clock frequency fa. Thereby, an audio signal which hasbeen time-base-decompressed as before can be obtained.

FIG. 11 is a diagram illustrating a state of time-base decompression bythe time-base decompression part 104. Data during a period in which thedemultiplexing control signal is LOW is taken as an audio signal, andthe time-base-compressed audio signal is inputted at the samplingfrequency fv only for the period in which the demultiplexing controlsignal is LOW and this signal is outputted at the sampling frequency fa,thereby obtaining the time-base-decompressed audio signal.

Next, an operation of the audio clock reproduction part 105 will bedescribed. At the receiving end, on the basis of the video clock thathas been transmitted from the transmitting end, a PLL (Phase Lock Loop)control is performed to reproduce the audio clock, and the audio clockis supplied to the time-base decompression part 104.

As described above, in the signal transmission system according to thefirst embodiment of the present invention, the multiplexing part 102 atthe transmitting end multiplexes the video signal and the time-basecompressed audio signal on the basis of the multiplexing control signal,whereby the video signal and the audio signal can be transmitted throughthe same data line 106. Further, at the receiving end, the video/audiomultiplexed signal, which has been received through the data line 106,can be demultiplexed into the video signal and the audio signal inaccordance with the demultiplexing control signal.

Further, the horizontal synchronizing period or vertical synchronizingperiod of the video signal is employed as the multiplexing controlsignal and the demultiplexing control signal, and the audio signal istime-base-compressed at the transmitting end and time-base-decompressedat the receiving end, whereby the audio signal can be multiplexed inblanks of the video signal and separated therefrom.

Embodiment 2

Hereinafter, a signal transmission system according to a secondembodiment will be described with reference to FIGS. 12 to 19.

FIG. 12 is a diagram illustrating a structure of the signal transmissionsystem according to the second embodiment.

In FIG. 12, a signal transmitter (transmitting end) comprises atime-base compression part 201, which time-base-compresses an audiosignal, a multiplexing part 202, which multiplexes a video signal andthe audio signal employing a multiplexing control signal and outputs avideo/audio multiplexed signal, and a multiplexing control signalprocessing part 208, which processes the multiplexing control signal.

A signal receiver (receiving end) comprises a demultiplexing part 203,which demultiplexes the video/audio multiplexed signal received througha data line 206, a time-base decompression part 204, whichtime-base-decompresses the audio signal obtained by the demultiplexingpart 203, and an audio clock reproduction part 205, which reproduces anaudio clock from a video clock received from the transmitting endthrough a clock line 207.

The data line 206 is a transmission line connecting the signaltransmitter and the signal receiver.

The signal transmission system according to the second embodimentdiffers from the signal transmission system of the first embodiment inthat the multiplexing control signal is not given to the receiving endin the signal transmission system according to the second embodiment.

Hereinafter, an operation of the signal transmission system according tothe second embodiment will be described. The time-base compression part201 time-base-compresses the audio signal like in the first embodiment,while the multiplexing control signal for the time-base compression isdifferent from that in the first embodiment.

FIG. 13 is a diagram illustrating a structure of the time-basecompression part 201 (memory). The time-base compression part 201 isconstituted by a memory like the time-base compression part 101 of thefirst embodiment, and converts a sampling rate of the audio signal. Inthe first embodiment, as the control signal for this memory, themultiplexing control signal, i.e., the horizontal synchronizing signalor the vertical synchronizing signal is used as it is, while in thissecond embodiment this multiplexing control signal is somewhat processedto be employed. More specifically, a signal which falls after counting avideo sampling clock during an L-clock period (L×1/fv sec.) sincefalling of the multiplexing control signal (horizontal synchronizingsignal or vertical synchronizing signal) is employed. The object of thisprocessing is to provide a no-signal period (L-clock period) before theaudio signal after the time-base compression, and make this no-signalperiod recognized at the receiving end as a switching timing between thevideo signal and the audio signal.

FIG. 14 is a diagram illustrating a state of time-base compression bythe time-base compression part 201. In this figure, the relationshipbetween the audio signal before the time-base compression and the audiosignal after the time-base compression is almost the same as that in thefirst embodiment, while the audio signal after the time-base compressionis delayed from the falling of the multiplexing control signal by Lclocks. This L-clock period is in a no-signal state.

FIG. 15 is a diagram illustrating a state of multiplexing of the videosignal and the audio signal in the second embodiment. As shown in FIG.14, an L-clock no-signal period is provided between the video signal andthe time-base-compressed audio signal. In this second embodiment,samples of the time-base-compressed audio signal that is to bemultiplexed with the video signal are defined as a video sampling clockof a M-clock period (M×1/fv sec.). Variables L and M are integers havingfixed values. The multiplexing control signal processing part 208generates a new multiplexing control signal which is obtained bydelaying the fall of the multiplexing control signal (horizontalsynchronizing period or vertical synchronizing period) by L clocks.Accordingly, the positions and the number of sampling points of theaudio signal can be recognized at the receiving end, thereby separatingthe audio signal.

FIG. 16 is a diagram illustrating a structure of the demultiplexing part203. In this figure, numeral 210 denotes a selector circuit, whichdemultiplexes the multiplexed signal into the video signal and thetime-base-compressed audio signal. Numeral 211 denotes a selectorcontrol signal generation part, which generates a signal for controllingthe selector circuit 210. Numeral 212 denotes a no-signal detectionpart, which detects a no-signal state of the video/audio multiplexedsignal transmitted through the transmission line. A counter 213 counts aperiod during which samples of the audio signal exist, i.e., an M-clockperiod (M×1/fv sec.).

Next, a specific operation of the demultiplexing part 203 will bedescribed. When detecting a no-signal state of the L-clock period(L×1/fv sec.), the no-signal detection part 212 changes its output levelfrom HIGH to LOW. A timing of the start of counting by the counter 213(falling of the output) is the same as a timing of the falling of theoutput from the no-signal detection part 212. When counting the M-clockperiod since the fall of the output from the no-signal detection part212, the counter 213 raises its output from LOW to HIGH. The selectorcontrol signal generation part 211 is a circuit for calculating an OR(logical add) of the output from the no-signal detection part 212 andthe output from the counter 213. The selector circuit 210 selects A toextract the video signal in a period during which the output from theselector control signal generation part 211 is HIGH, while selecting Bto extract the time-base-compressed audio signal in a period duringwhich the output from the selector control signal generation part 211 isLOW.

FIG. 17 illustrates a state of demultiplexing of the video signal andthe audio signal in the second embodiment. In the video/audiomultiplexed signal on the transmission line, the no-signal statecontinues for the L-clock period, and thereafter the audio signalsamples exist for the M-clock period. As shown in FIG. 16, the selectoris switched to select B in the period during which the selector controlsignal is LOW and set at A in other cases, whereby the video signal andthe audio signal can be separated and extracted from the video/audiomultiplexed signal.

FIG. 18 is a diagram illustrating a structure of the time-basedecompression part 204. The time-base decompression part 204 isconstituted by a memory, like the time-base decompression part 104 inthe first embodiment, while the selector control signal shown in FIG. 16is employed as the demultiplexing control signal.

FIG. 19 is a diagram illustrating a state of time-base decompression bythe time-base decompression part 204 (memory). The time-base-compressedaudio signal is inputted to the time-base decompression part 204 at thesampling frequency fv only in a period during which the demultiplexingcontrol signal, that is, the selector control signal is LOW, and theinputted signal is outputted at the audio sampling clock fa, therebyobtaining the time-base-decompressed audio signal.

As described above, the signal transmission system according to thesecond embodiment can realize the same effect as that of the signaltransmission system according to the first embodiment, withouttransmitting the multiplexing control signal to the receiving end. Thatis, in this second embodiment, the no-signal state in the L-clock periodis provided between the video signal and the audio signal in the periodduring which the video signal and the audio signal are multiplexed, andthe sample points of the audio signal are kept constant as the M-clockperiod, and the receiving end detects the L-clock period of theno-signal state and thereafter takes the M-clock period as a timing ofseparating the audio signal. Accordingly, the audio signal and the videosignal can be separated, without transmitting the multiplexing controlsignal to the receiving end.

Embodiment 3

Hereinafter, a signal transmission system according to a thirdembodiment will be described with reference to FIGS. 20 to 23. In thethird embodiment, the signal transmission system according to the firstor second embodiment is applied to the DVI (Digital Visual Interface)standard.

FIG. 20 is a diagram illustrating a structure of the signal transmissionsystem according to the third embodiment.

In FIG. 20, numeral 301 denotes a time-base compression part, which isthe same as that employed in the first or second embodiment. Numeral 302denotes a demultiplexing part, which demultiplexes atime-base-compressed audio signal into signals CTL 2, CTL 3 and CTL 1according to the DVI standard, to be superimposed. Numerals 303 to 305denote TMDS encoders/serializers and numerals 306 to 308 denote TMDSdecoders/recoveres, which are the same as those in the prior art.Numeral 309 denotes a composition part, which composes the audio signalsobtained from the signals CTL 1, 2, and 3. Numeral 310 denotes atime-base decompression part, which decompresses thetime-base-compressed audio signal that is outputted from the compositionpart 309. In this figure, serial data of time-division-multiplexed BLUEand HSYNC or VSYNC (horizontal synchronizing period or verticalsynchronizing period) of a video signal are transmitted through channel0 of a transmission line, serial data of time-division-multiplexed GREENand audio (CTL 1) is transmitted through channel 1, and serial data oftime-division-multiplexed RED and audio (CTL 2, 3) is transmittedthrough channel 2.

An operation of the so-configured signal transmission system will bedescribed.

FIG. 21 illustrates states of signals on the transmission linesaccording to the third embodiment.

First, input data to the TMDS encoders are shown on the top. CTLs(Control Signals) are inserted when a DE (data enable) signal is LOW,and the time-base-compressed audio signals are superimposed on theseCTLs 1, 2 and 3, thereby TMDS-encoding the signals. As signals on thetransmission lines, the encoded CTLs 2 and 3 are superposed in channel2, and the encoded CTL 1 is superposed in channel 1. Thus, on thetransmission line, audio (audio signal) is superposed in the period ofthe horizontal synchronizing signal or the vertical synchronizingsignal. Data, which is TMDS-decoded and recovered at the receiving end,is shown at the bottom. This recovered data is identical to the inputdata at the transmitting end.

Next, a method for separating audio at the receiving end will bedescribed.

As shown in FIG. 22, a prescribed period of the data in channel 0 isinitially detected by a data prescribed period detection circuit 350(data prescribed period detector). This prescribed period of the data isa horizontal synchronizing period or a vertical synchronizing period.This prescribed period of the data is detected to generate a DE (DataEnable) signal, a period during which the DE signal is LOW is taken as aperiod during which the audio signal is multiplexed, the DE signal issupplied to the decoding and video/audio demultiplexing circuits 351(channel 1 decoder, video/audio demultiplexer) and 352 (channel 2decoder, video/audio demultiplexer) for channels 1 and 2, and the videosignal and the audio signal are separated by channel 1 and 2 decoders.Then, the audio signals of the separated lines (CTL 1, CTL 2, and CTL 3)are obtained.

Next, a decoding method at the receiving end will be described.

In FIG. 23, the video/audio multiplexed signal that has been transmittedthrough channel 2 is subjected to serial/parallel conversion by aserial/parallel conversion circuit 360 (serial/parallel converter), thissignal is taken as a video signal during the period in which the DE(Data Enable) signal is HIGH, and the video signal is subjected to 10bit/8 bit TMDS decoding by a decoder 362, thereby obtaining a REDsignal. On the other hand, this signal is taken as an audio signalduring the period in which the DE (Data Enable) signal is LOW, and theaudio signal is subjected to 10 bit/2 bit TMDS decoding by a decoder363, thereby obtaining audio signals in the lines of CTL 2 and CTL 3.Similarly in channel 1, the transmitted video/audio multiplexed signalis subjected to serial/parallel conversion by a serial/parallelconversion circuit 361 (serial/parallel converter), this signal is takenas a GREEN video signal during the period in which the DE (Data Enable)signal is HIGH, and the video signal is subjected to 10 bit/8 bit TMDSdecoding by a decoder 364. On the other hand, during the period in whichthe DE (Data Enable) signal is LOW, this signal is subjected to 10 bit/2bit TMDS decoding by a decoder 365, thereby obtaining the audio signalfor the CTL 1.

In this way, the audio signals which are obtained on the CTL (Control)lines are composed by the composition part 309 and further subjected torate conversion by the time-base decompression part 310, therebyobtaining the original audio signal.

Next, operations of the demultiplexing part 302 and the composition part309 will be described.

In the demultiplexing part 302, the time-base-compressed audio signal isdemultiplexed into the three lines of CTL 2, 3 and 1, while only a lineof CTL 2 or two lines of CTL 2 and 3 may be used depending on the bandof the audio signal. In addition, the audio signal may be separated inthe order of CTL 2, 3, 1, 2, 3 and 1, according to the order of samplingpoints of the audio signal. In the composition part 309, the decodedaudio signals transmitted through the transmission lines are consideredthat the audio signals are transmitted in the order of CTL 2, 3 and 1,thereby to compose the audio signals. These three lines can be used notonly in this order of CTL 2, 3 and but also in an arbitrary order, whilethe order of demultiplexing and composition should be decided at thetransmitting end and the receiving end.

As described above, in the signal transmission system according to thethird embodiment, the structure of the signal transmission systemaccording to the first or second embodiment is applied for the DVIstandard. The time-base-compressed audio signal is demultiplexed intothe lines of CTL 2, 3 and 1, and at the receiving end, the audio signalstransmitted by the CTL 2, 3, and 1 are composed to betime-base-decompressed so as to restore the audio signal. Thus, theaudio signal can be also transmitted by a signal transmission systemaccording to the DVI standard which can conventionally transmit onlyvideo.

Embodiment 4

Hereinafter, a signal transmission system according to a fourthembodiment will be described with reference to FIGS. 24 and 25. Thefourth embodiment differs from any of the first to third embodiments. Inthis fourth embodiment, an audio signal is not transmitted by employingblanks in a video signal like in the first to third embodiments, but oneof three transmission lines that are employed in a signal transmissionsystem of the DVI standard is reserved as a transmission line for audiosignal. That is, in the case of the DVI standard, transmission of thevideo signal is performed for component signals such as RED, GREEN andBLUE, while in the fourth embodiment, a mode in which transmission isperformed with Y-color difference signals such as Y, Pb and Pr is added,and then an unused channel is allocated for the audio signal.

FIG. 24 is a diagram illustrating a structure of the signal transmissionsystem according to the fourth embodiment.

In this figure, numeral 401 denotes a selector, which selects a REDsignal or a luminance signal (Y), and supplies the selected signal to aTMDS encoder. Numeral 402 also denotes a selector, which selects a GREENsignal or a Pb/Pr signal. Numeral 403 denotes a selector, which selectsone of a BLUE signal and an audio signal. Numerals 404 to 406 denoteTMDS encoders/serializers and numerals 407 to 409 denote TMDSdecoders/recoveres. These constituents are identical to those of thefirst to third embodiments.

The characteristic of this fourth embodiment is the use of Ycolor-difference transmission for transmitting video signals. As the Ycolor-difference transmission, there is, for example, 4:2:0transmission. The 4:2:0 transmission is one in which the color signalrate is a half of the luminance signal rate, as shown in FIG. 25. Morespecifically, the number of samples of the color signal is a half of thenumber of samples of the luminance signal. Thereby, the video signal canbe transmitted on two channels through the transmission lines of the DVIstandard. More specifically, the luminance signal is transmitted onchannel 2, and the color signal Pb/Pr is transmitted on channel 1. Theaudio signal is superimposed in unused channel 0. This audio signal isthe original audio signal which is not time-base-compressed.

As described above, the signal transmission system according to thefourth embodiment further has the mode in which the transmission isperformed with the Y color-difference signals such as Y, Pb and Pr, andan unused channel is allocated to the audio signal, thereby realizing asignal transmission system compliant with the DVI standard, in which theaudio signal as well as the video signal can be transmitted.

Further, in the fourth embodiment, Y, Pb/Pr, and audio signals areallocated to channel 2, channel 1, and channel 0, respectively, but theallocation is not restricted to the above-mentioned manner.

Further, in the embodiments according to the present invention,multiplexing and transmission of signals are performed by themultiplexing part, but the multiplexing and transmission can beperformed separately by different components.

A signal transmitter and a signal receiver according to the presentinvention are available as a signal transmission system compliant withthe DVI standard, which can transmit an audio signal as well as a videosignal.

1. A signal receiver, which is connected to a signal transmitter via atransmission line, and which is compatible with DVI compliant sources,the signal receiver comprising: a receiving unit receiving a pluralityof signals via the transmission line connected thereto, the transmissionline, from which the receiving unit receives the plurality of signals,including: a first channel transmitting a first multiplexed signal inwhich a first digital video signal, a first time-axis compressed digitalaudio signal, and a first control signal are multiplexed, such that thereceiving unit receives the first multiplexed signal; a second channeltransmitting a second multiplexed signal in which a second digital videosignal, a second time-axis compressed digital audio signal, and a secondcontrol signal are multiplexed, such that the receiving unit receivesthe second multiplexed signal; and a third channel transmitting a thirdmultiplexed signal in which a third digital video signal, and asynchronizing signal are multiplexed, such that the receiving unitreceives the third multiplexed signal; and a separation unit separating(i) the first time-axis compressed digital audio signal from thereceived first multiplexed signal based on the first control signalreceived by the receiving unit and the second control signal received bythe receiving unit, and (ii) the second time-axis compressed digitalaudio signal from the received second multiplexed signal based on thefirst control signal received by the receiving unit and the secondcontrol signal received by the receiving unit.
 2. The signal receiver asrecited in claim 1, wherein the separation unit separates (i) the firsttime-axis compressed digital audio signal and the first digital videosignal from the received first multiplexed signal based on the firstcontrol signal received by the receiving unit and the second controlsignal received by the receiving unit, and (ii) the second time-axiscompressed digital audio signal and the second digital video signal fromthe received second multiplexed signal based on the first control signalreceived by the receiving unit and the second control signal received bythe receiving unit.
 3. The signal receiver as recited in claim 2,wherein the receiving unit further receives a first sampling clock ofthe first digital video signal from the signal transmitter, and whereinthe signal receiver further includes an audio clock reproduction unitthat reproduces an audio clock based on the first sampling clock of thefirst digital video signal.